Systems of the type stated at the outset are already known from the prior art and are used in line systems, the lines of which carry liquids which may freeze at low ambient temperatures. In a line system of this kind, it is customary to heat the individual hose lines and the plug-in connectors to prevent the liquid carried in the hose lines from freezing. Line systems with heated hose lines and heated plug-in connectors are used, for example, in windscreen washer systems and in line systems for a urea solution, which is used as an NOx reduction additive for diesel engines with SCR catalytic converters.
A system for connecting hose lines of the type stated at the outset is known from DE 10 2005 050 867 A1, for example. The plug-in connector known from this publication has a housing, into which a plug is inserted, the plug containing a heating element and two contact elements, via which the heating element is connected to an electric power source. The heating element is used to heat only the section of the plug-in connector in which the housing is situated. In the publication mentioned, there is therefore also a proposal to provide the heating element with a heating lance, which projects into the tube of the plug-in connector and there directly heats the liquid passed through the plug-in connector. The provision of the heating lance enables the liquid to be heated up reliably. However, it is noted that the structure of the system known from DE 10 2005 050 867 A1 is complex. Moreover, the heating lance must be guided into the interior of the plug-in connector, starting from the heating element, and this may lead to problems with the tightness of the plug-in connector.
United States patent application publication 2010/0290764 likewise discloses a system for connecting hose lines. In the system known from this publication, the tube of the plug-in connector is wound with an electrically conductive wire, which serves as an electric heating element. Guide elements for the heating wire are provided on the surface of the tube of the plug-in connector. To provide mechanical protection for the heating wire, the plug-in connector can either be overmolded or provided with an encapsulation. With the system known from United States patent application publication 2010/0290764 for connecting hose lines, the plug-in connector can be heated over the entire length thereof, thereby reliably preventing the liquid that is passed through the plug-in connector from freezing. However, the system known from this publication is complex to produce for a number of reasons. Thus, for example, separate guide elements for the heating wire must be provided on the surface of the tube of the plug-in connector. Furthermore, the heating wire must be passed over the individual guide elements in tight coils, a complex procedure that is possible only with difficulty, if at all, in an automated process. Finally, it must be noted that there is a risk of damage to the system even during the production thereof. For example, the heating wire is passed over the guide elements with tight bending radii, and this may cause damage to the heating wire. In addition, the overmolding of the plug-in connector can also cause damage to the sensitive heating wire.